THE PRIME NUMBER RIDDLE

Trending Tags

Feel free to use content on this page for your website or blog, we only ask that you reference content back to us. Use the following code to link this page:
Terms · Privacy · Contact
Riddles and Answers © 2022

The Prime Number Riddle

Two hundred people in an auditorium are asked to think of a single digit number from 1 to 9 inclusive and write it down. All those who wrote down a prime number are now asked to leave. Ninety people remain behind in the hall. How many of these are expected to have written down an odd number?
Hint: Remember that 1 is not a prime number.
Those that remain behind must have written {1,4,6,8,9} and from this only {1,9} are odd. The probability of an odd number is thus 2/5.
Expected number of odds is 2/5 * 90 = 36
Did you answer this riddle correctly?
YES  NO  

Add Your Riddle Here

Have some tricky riddles of your own? Leave them below for our users to try and solve.